Microdisplay projection systems typically employ a transmissive or a reflective microdisplay imager, commonly referred to as a light valve or light valve array, which imposes an image on an illumination light beam. One of the important advantages on reflective light valves over transmissive light valves is that reflective light valves permit controlling circuitry to be placed in situ behind the reflective surface, and more advanced integrated circuit technology is available because the substrate materials are not limited by their opaqueness.
Reflective liquid-crystal-on-silicon (LCOS) imagers rotate while modulate the polarization of incident light. Thus, polarized light is either reflected by the LCOS imager with its polarization state substantially unmodified, or with a degree of polarization rotation imparted to provide a desired grey scale. Accordingly, a polarized light beam is generally used as the input beam for reflective LCOS imagers, while a polarization beam splitter (PBS) is typically employed for splitting the incoming light beam to two polarized light beams in orthogonal polarization states.
Widely used for various portable and handheld micro projection display applications, a single-imager engine employs one LCOS modulation imager and one PBS. One of the most obvious drawbacks of this optical projection engine is that only limited portion of illumination light in one polarization state is used for illuminating the LCOS imager and therefore, after modulation and reflection by the LCOS imager, total illumination projected through a projection lens system onto a projection screen is limited, which results in low optical efficiency.